[Bug ada/64492] Disabling libada prevents building gnattools-cross

["simon at pushface dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64492

--- Comment #13 from simon at pushface dot org ---
(In reply to Luke A. Guest from comment #2)
> But, I noticed this in the gnat makefile a while back and was going to
> investigate, but haven't got around to it yet:
> 
> # *-elf, *-eabi, or *-eabispe
> ifeq ($(strip $(filter-out elf eabi eabispe,$(target_os))),)
>   TOOLS_TARGET_PAIRS=\
>   mlib-tgt-specific.adb<mlib-tgt-specific-xi.adb \
>   indepsw.adb<indepsw-gnu.adb
> endif
> 
> Essentially, we just need for that to include a specific system or build
> with just those two files and it's sorted.

TOOLS_TARGET_PAIRS is set in both gnattools/Makefile (when it has been
configured) and gcc/ada/gcc-interface/Makefile.in. Your patch is to the
gnattools/ one, the gcc-interface one already has this pair.

If it is the case that any arm-*-eabi target is going to be a bare runtime
target, with --disable-libada disabling gnattools/, then Ericâs patch and
Arnoâs incantation will IMO work - I just built GCC 5 arm-eabi with Ericâs
patch and the two files were successfully copied into build/gcc/ada/tools, and
arm-eabi-gnatmake is capable of building a library. Havenât checked the map
feature yet.

Looking at the two versions of TOOLS_TARGET_PAIRS, it seems that
gcc-interface/Makefile is mainly concerned with building the RTS
(LIBGNAT_TARGET_PAIRS etc) with the TOOLS_TARGET_PAIRS being left in place,
pretty much as fossils, when building the tools was moved to
gnattools/Makefile.